Add WorkerPool::PostTaskAndReply and use in DHCP code.

base/threading/worker_pool.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_THREADING_WORKER_POOL_H_
 #define BASE_THREADING_WORKER_POOL_H_
 #pragma once
 
 #include "base/base_export.h"
 #include "base/callback.h"
@@ skipping 20 matching lines @@
   // should be used for tasks that will take a long time to execute.  Returns
   // false if |task| could not be posted to a worker thread.  Regardless of
   // return value, ownership of |task| is transferred to the worker pool.
   //
   // TODO(ajwong): Remove the Task* based overload once we've finishsed the
   // Task -> Closure migration.
   static bool PostTask(const tracked_objects::Location& from_here,
                        Task* task, bool task_is_slow);
   static bool PostTask(const tracked_objects::Location& from_here,
                        const base::Closure& task, bool task_is_slow);
+
+  // Just like MessageLoopProxy::PostTaskAndReply, except the destination
+  // for |task| is a worker thread and you can specify |task_is_slow| just
+  // like you can for PostTask above.
+  static bool PostTaskAndReply(const tracked_objects::Location& from_here,
+                               const Closure& task,
+                               const Closure& reply,
+                               bool task_is_slow);
 };
 
 }  // namespace base
 
 #endif  // BASE_THREADING_WORKER_POOL_H_